The invention relates generally to dry etching of indium and tin oxides.
The manufacture of a flat glass panel display, for example, typically begins with a clean glass substrate. Transistors are formed on the flat panel using film deposition and selective etching techniques. Sequential deposition, photo-lithography and selective etching of film layers on the substrate create individual transistors on the substrate. These devices, as well as metallic interconnections, liquid crystal cells and other devices formed on the substrate are then used to create active matrix display screens on the substrate to create a flat panel display in which display states are electrically created in the individual pixels.
Opto-electronic devices such as liquid crystal displays (LCD's), charge coupled sensor devices (CCD's) and the like often include thin-film transparent electrodes disposed over a light transmitting or light receiving element.
The transparent electrodes are typically composed of an oxide of indium (InO) or an oxide of tin (SnO) or a mixture of these oxides or a compound having the general formulation: In.sub.x Sn.sub.y O.sub.z, where the z factor is greater than zero but less than 100% and where the sum x+y fills the remainder of the 100%. The formulation, In.sub.x Sn.sub.y O.sub.z is commonly known in the art as ITO.
During manufacture, a thin-film of the material making up the transparent electrodes is deposited on a substrate. The thin-film is thereafter selectively etched so as to remove pre-specified portions and thereby define a desired wiring pattern.
It is generally desirable in mass-production situations to etch the transparent-electrode thin-film in such a way that the etching does not significantly damage any underlying structures.
It is also generally desirable to perform the etch as quickly as possible and with as few steps as necessary in order to reduce mass-production complexity and costs.
Until recently, one common method for selectively etching ITO was to wet etch through a photolithographically patterned mask using chemically-reactive aqueous agents such as ferric chloride (FeCL.sub.3)
Wet etching, however, has drawbacks. It tends to leave a liquid residue, which often must be removed prior to further processing. The removal of residue complicates the overall process and increases costs.
Another drawback of wet etching is that its material removal rate tends to be highly sensitive to temperature variations. Tight temperature control, which also complicates the overall process and increases costs, is needed to compensate and prevent over or under etching. "Under etching" refers to the condition where the transparent-electrode thin-film is not etched through thoroughly and undesired shorts appear in the resultant conductor pattern. "Over etching" refers to the condition where the transparent-electrode thin-film is etched through thoroughly and undesired etching of the underlying substrate begins and/or time and resources are wasted in trying to etch to a depth beyond that needed.
Yet a further drawback of wet etching is that it is isotropic. Over etching may lead to undesired undercutting beneath the etch mask. The undercutting may be so extensive that it leads to unintended open circuits in the conductor pattern.
More recently, attempts have been made to overcome the problems of wet etching by dry etching the material layer of the thin-film transparent electrodes with an anisotropic reactive plasma.